1. Field of the Invention.
The invention pertains to the iceA gene of Helicobacter pylori and to the antigenic polypeptides encoded by the genes, as well as methods of using the gene and polypeptides to diagnose H. pylori infection and predisposition to peptic ulceration and other diseases associated with H. pylori infection.
2. Background Art
Helicobacter pylori infection causes chronic superficial gastritis (1), and may lead to duodenal and gastric ulcer disease, gastric adenocarcinoma, or non-Hodgkins lymphoma of the stomach (2-4). However, most infected persons remain asymptomatic, with only 10-20% of infected persons developing one of these illnesses (5). One putative virulence factor elaborated by 40-60% of H. pylori isolates is a toxin, encoded by vacA, that induces vacuolation of eukaryotic cells and injury to gastric epithelium (6,7). Another strain-specific H. pylori constituent is the 120-132 kDa cytotoxin-associated gene A (cagA) product which is present in 60% of strains (8,9). Although cagA genotype and cytotoxin expression both are associated with peptic ulcer disease (8,10,11), the majority of persons infected with such strains do not progress to ulceration, suggesting that other H. pylori genes also are important in disease pathogenesis.
The extensive genomic diversity that exists among H. pylori isolates (12) hinders identification of putative strain-specific virulence determinants. Another factor that may limit detection of genes relevant to pathogenesis is that bacterial transcripts expressed during growth in vitro may not reflect in vivo expression (13). Because so little is known about the pathogenesis of H. pylori, there is a need to identify genes expressed selectively in ulcer-causing strains.
The present invention meets this need by demonstrating that adherence to gastric epithelial cells induces the selective expression of a novel H. pylori gene, iceA (induced by contact with epithelium), that is highly correlated with peptic ulcer disease. iceA exists in two major allelic variants which are not associated with previously described H. pylori virulence determinants.
Previous methods used to identify genes that are selectively expressed under specific environmental conditions have relied largely on subtractive hybridization techniques (35). In contrast, the current experiments demonstrate that RAP RT-PCR is an effective approach for the identification of a conditionally expressed gene in H. pylori. The current method provide a means by which induction of prokaryotic virulence genes by be identified following stimulation with factors that actually reflect in vivo pathogenesis. Having shown this, the use of RAP RT-PCR therefore could be extended to other bacteria to identify up-regulation of undescribed genes that may reflect pathogenetic mechanisms.